chore(docker): update build image to go 1.12.7

update build image to golang 1.12.7
update base image to alpine 3.10

Signed-off-by: mritd <mritd@linux.com>

Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.12.5-alpine3.9 AS builder
+FROM golang:1.12.7-alpine3.10 AS builder
 
 ENV GO111MODULE on
 ENV GOPROXY https://goproxy.io
@@ -7,7 +7,7 @@ RUN apk upgrade \
     && apk add git \
     && go get github.com/shadowsocks/go-shadowsocks2
 
-FROM alpine:3.9 AS dist
+FROM alpine:3.10 AS dist
 
 LABEL maintainer="mritd <mritd@linux.com>"